1. Field of the Invention
The present invention relates to a die bonding apparatus.
2. Description of the Prior Art
Conventionally, there has been well known a die bonding apparatus for automatically bonding a semiconductor die onto a bonding surface of a semiconductor lead frame.
A conventional bonding apparatus as disclosed in Japanese Patent Application No. 62-271537 will be described hereinbelow by way of example.
FIG. 1 is a diagrammatical side view showing the above-mentioned conventional die bonding apparatus. In the drawing, a motor 52 is mounted on a base 51a formed at the upper portion of an arm 51. A rotary shaft 52a of this motor 52 is directly connected to a screw 53, and this screw 53 is screwed into a collet head 54. In the construction as described above, when the motor 52 is driven, the collet head 54 can be moved up and down.
Further, a vertical through hole is formed in a body portion 54a of the collet head 54, and a collet shaft 55 is fitted into this through hole so as to be slidable in the vertical direction. A stopper 56a is attached to the collet shaft 55 on the upper portion thereof, and a collet 12 is attached to the collet shaft 55 on the lower portion thereof to suck and support a semiconductor die 2. In addition, a spring support member 56b is provided near the lower portion of the collet shaft 55, and a spring 59 is interposed between the spring support member 56b and the body portion 54a of the collet head 54. In the construction as described above, it is possible to press the semiconductor die 2 onto the semiconductor lead frame 1 under a constant pressure determined by an elastic force of the spring 59 (referred to as bonding pressure, hereinafter), whenever the semiconductor die 2 is bonded onto the semiconductor lead frame 1.
Further, on the upper portion of the collet head 54, a gap sensor 60 is provided to detect the contact between the semiconductor die 2 and the semiconductor lead frame 1. In more detail, when the semiconductor die 2 is not in contact with the semiconductor lead frame 1, since the collet shaft 55 is urged in the downward direction by the spring 59, this gap sensor 60 is in contact with the stopper 56a. On the other hand, when the collet head 54 is lowered for bonding so that the semiconductor die 2 is brought into contact with the semiconductor lead frame 1 and further pressed onto the semiconductor lead frame 1, since the collet shaft 55 is moved in the upward direction relative to the collet head 54, a gap is produced between the gap sensor 60 and the stopper 56a. Accordingly, it is possible to detect the contact between the semiconductor die 2 and the semiconductor lead frame 1. Further, a predetermined bonding pressure can be applied to the semiconductor die 2 by rotating the motor 52 by a predetermined angular stroke after the gap sensor 60 has detected the contract between the semiconductor die 2 and the semiconductor lead frame 1.
In the conventional bonding apparatus as described above, however, there exist the following drawbacks:
(1) The contact between the semiconductor die 2 and the semiconductor lead frame 1 can be detected on the basis of whether the gap sensor 60 is brought into contact with the stopper 56a. In this construction, however, since a gap between the gap sensor 60 and the stopper 56a is produced only after the spring 59 has been compressed to some extent, a detection error occurs inevitably. Further, the inventors have confirmed that this detection error fluctuates according to change in the downward travel speed of the semiconductor die 2 when the semiconductor die 2 is brought into contact with the semiconductor lead frame 1, with the result that it is difficult to compensate for the above-mentioned detection error and thereby the bonding pressure applied to the semiconductor die 2 fluctuates away from a predetermined set value. Further, since this detection error is produced inevitably, it has been substantially impossible to detect whether the thickness of paste used for bonding lies within an allowable thickness range or not, thus deteriorating the production yield of the die bonding process.
(2) In the conventional die bonding apparatus, mechanical parts 55 to 59 must be provided for applying bonding pressure to the semiconductor die 2, in addition to the mechanical parts 51 to 55 for moving the collet 12 up and down as described above. Therefore, the conventional die bonding apparatus involves various shortcomings as follows: the apparatus is complicated in mechanism, large in volume and heavy in weight, and further high in manufacturing cost.
(3) Further, since the weight of the arm 51 is large, the travel speed of the arm 51 is slow when the arm 51 is moved over the semiconductor lead frame 1 after the semiconductor die 2 has been supported by the collet 12, thus causing a difficulty in improvement of the processing capacity (the number of semiconductor dies bonded for each unit time).
(4) Since the apparatus is heavy, the vertical motion of the collet head 54 cannot follow the rotary motion of the motor 52 accurately, with the result that the collet head 54 has been moved excessively or vibrated. Therefore, when the semiconductor die 2 is sucked to by the collet 12 or when the semiconductor die 2 sucked by the collet 12 is brought into contact with the semiconductor lead frame 1, an excessive shock is inevitably applied to the semiconductor die 2, so that there exists a problem in that the semiconductor die 2 may be damaged.